A control device and a method for an emergency steering support function of a land vehicle are described. In particularly, a control device and a method for calculating an avoidance trajectory are described.
Systems are known from the prior art that activate the brakes of a vehicle in critical driving situations in order to avoid a collision with an obstacle or in order to at least reduce the collision speed. Since the length of the braking distance rises disproportionally with increasing speed, emergency braking systems have the drawback that they cannot always prevent a collision, for example in the event of a large differential speed between vehicle and obstacle, but rather they can only reduce the severity of the collision.
Since collisions can be effectively avoided even at high speeds through an evasive maneuver, emergency avoidance can be safer and more effective than automatic emergency braking in some driving situations. However, the vehicle can be brought into the limit range of the vehicle dynamics. Inexperienced drivers are often unable to cope with the respective hazard situations and are often incapable of successfully and properly executing the emergency evasive maneuver. Rather, the danger exists of the driver making an incorrect steering movement and then losing control of the vehicle. The driver should therefore be supported in an emergency evasive maneuver.
In this regard, an emergency avoidance system for motor vehicles is proposed in document DE 10 2004 008 894 A1. The system comprises an evaluation unit that determines at least one avoidance trajectory and/or at least one automatic emergency braking maneuver. After the initiation of the driving maneuver, an avoidance trajectory is communicated to the driver in the form of a steering-wheel torque applied by a suitable steering system. The driver can follow the suggested avoidance trajectory or steer past the applied steering-wheel torque.
A method and a device for executing an avoidance trajectory are known from document DE 10 2008 013 988 A1. The avoidance trajectory is calculated here as a so-called sigmoid function. To increase the stability of the vehicle during the evasive maneuver, a provision is made that a steering system combines a front-wheel steering function and a rear-wheel steering function in such a way that the front wheels and the rear wheels of the vehicle are controlled in the same direction.
A method and a device for steering a motor vehicle are known from document EP 1 926 654 B1. An avoidance trajectory is calculated and a control output signal is established in accordance with a deviation between an actual position and the target position prescribed by the avoidance trajectory in at least two linear control modules arranged in parallel. A trajectory specification in the form of a sigmoid has proven especially advantageous. The output signals of the parallel linear controllers are weighted as a function of the driving speed, and a steering angle is determined on the basis of the weighted controller output signals.
A method for avoiding the collision of a vehicle with at least one object or at least reducing the consequences thereof is known from document WO 2008/031662 A1. Using the sensor system of the vehicle, the current vehicle state and objects in the sensor detection range are identified. In consideration of the current vehicle state, an avoidance trajectory is determined from the totality of all possible movements of the vehicle by means of an optimization function. As soon as a driver avoidance reaction is determined, control signals for correcting the vehicle state are generated in such a way that the vehicle is guided in the direction of the avoidance trajectory.
A method for steering support in emergency maneuvers is known from document EP 2 323 890 B1. A trajectory calculation unit calculates driving lines of all drivable and stable movement trajectories. Upon identification of a hazard situation, the movement trajectory that corresponds to the driving maneuver indicated by the current steering wheel actuation is identified from the currently determined driving lines. The current steering angle is compared as an actual value to a target value determined from a determined avoidance trajectory. If the control deviation exceeds a predetermined value, the current steering angle is compensated by means of an additional steering angle and/or the required steering angle is communicated to the driver by means of counter-torque applied to the steering wheel.
The document “Querregelung eines Versuchsfahrzeugs entlang vorgegebener Bahnen” [“Lateral control of a test vehicle along predetermined trajectories”] by Steffen Kehl, published by Shaker Verlag in 2007, discloses a trajectory slave control that guides the vehicle's center of gravity along a predetermined trajectory by steering the vehicle. The Intention of this trajectory slave control is to ensure the reproducibility of driving tests. In the trajectory slave control described in this document, the steering mechanism is used as an actuator and an Integrated navigation system is used for the measurement. Clutch, gear shifting, gas and brake continue to be controlled by the test engineer/driver. The target trajectory curvature required by the controller is established in the form of the coefficients of a polynomial vector defined in segments, the degree of the polynomials being selected such that, when the target trajectory is followed by the vehicle, no jumps occur in the steering angle speed.
In the known systems, the avoidance trajectory defining the target course of the evasive maneuver is frequently determined from a plurality of possible movement trajectories. However, these movement trajectories can only be calculated with great computational effort. The avoidance trajectories, the course of which is calculated by means of a sigmoid function, are not constant at the transitions from normal driving to evasive maneuver, thus resulting in jumps in their course that impair driver comfort and render difficult the controlling of the evasive maneuver.